Maintaining body temperature in a cold environment is key
for the survival of euthermic animals. In mammals, it is
achieved by both shivering and nonshivering thermogenesis.
Nonshivering thermogenesis is mainly mediated by brown adipose
tissue, in which chemical energy is dissipated in the form
of heat through the actions of uncoupling protein 1 (UCP1) in
mitochondria (1). In addition to its function to prevent hypothermia,
brown fat has also been of interest as a defense against
obesity and diabetes. Indeed, ablation of brown fat through
the use of a UCP1 promoter-driven toxin has shown that loss
of brown adipose tissue (BAT) causes an increased propensity to
weight gain and diabetes in experimental animals (2). Similarly,
ablation of UCP1 itself causes increased fat accumulation and
insulin resistance in mice, at least at thermoneutrality (3). Because
of the recent realization that adult humans have active brown fat
(4–6), UCP1-mediated thermogenesis has becoming a compelling
subject for research in obesity and other metabolic disorders.